In catalytic cracking of hydrocarbons, it is known that deposition of metals, such as nickel, vanadium, iron and the like, as contained in the starting hydrocarbons on the cracking catalyst used would lower the catalytic activity of the catalyst and additionally increase the amounts of hydrogen and coke formed to thereby decrease the yield of the desired useful components such as gasoline and so on. Accordingly, it has heretofore been known to use a so-called passivator of a compound of antimony, indium, bismuth or the like in catalytic cracking of hydrocarbons so as to passivate the aforesaid metals or to inactivate the same to thereby remove or reduce any harmful influence on the catalyst used, by various methods, for example, as described in U.S. Pat. Nos. 4,111,845, 4,153,536 and 4,257,919 and JP-A-104588 and 57-34188. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) In particular, it is known that various kinds of antimony compounds are excellent as the passivator for the purpose.
In addition to antimony trioxide and antimony pentoxide, such passivators include organic antimony compounds such as antimony tridecanoate, antimony tris(dithioacetate), antimony tris(p-toluenesulfonate), antimony tris(diphenylphosphite), antimony tris(o,o-dipropyldithiophosphate) and so on, which are described, for example, in JP-A-53-l04588. These passivators are used by dipping catalytic cracking catalysts in a solution containing the same or by adding the same to starting hydrocarbons.
Most of the organic antimony compounds are prepared by reaction of antimony trioxide in water or in an organic solvent. However, in accordance with the method of using such solvents, the reactor yield and, in its turn, the production yield are low. In particular, when water is used as a solvent, it is not easy to remove the water used from the reaction product formed, and the yield of the reaction product is also low. On the other hand, in order to obtain organic antimony compounds with high yield, for example, Czechoslovakian Pat. No. 221,707 illustrates a method of reacting antimony trioxide and a mercaptane in the presence of citric acid or salicylic acid. According to the said method, however, separation of such organic acid from the reaction product is not easy and the organic acid used would remain in the reaction product formed, so that it is difficult to obtain organic antimony compounds of high purity.